Difference to
recognize the diffent kind of controller:
If you look at the pins used to connect the Apple DISK II drives
you will recognize, that
at the bottom area of the FDC4 at the right connector there is
no area with 6 solderpads
for jumperblock, while at the AP53 that area is present.

In general it might be stated that the FDC4 is a "copycat" from
the IBS AP53 controller except of the fact that both controllers
differ by the contents within the eprom. This causes, that patch
software for FDC4 wonīt work correct with the AP53 and
vice versa.

I also canīt make any kind of prediction about the behaviour of
the AP53 if a eprom of the FDC4 is inserted. Up till now i have
never tested that behaviour, if a copy of the FDC4 eprom is
inserted in the AP53.

IBS AP53:

circuitplan:

manual
für Patch165 Disk:

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